Effect of urea introduced into feed on structural changes and mucopolisacharides content in branchial epithelium of rawbow trout (Salmo gairdneri Richardson)

Histochemical and histological surveys on gills of rainbow trout (Salmo gairdneri Rich.) fed control feed and feed with 2 and 4% of urea added were carried out. Irrespective of an urea amount added to feed, microscopic structure schedule of gills was identical. However, in case of some structural elements essential differences were noted, particularly for fish fed feed with 2% of urea added. Thickening of branchial epithelium on blood vessels side and increase in number and size of mucous cells were observed. Within the branchial epithelium mucous cells, the neutral mucopolisaccharides were most numerous for all experimental variants, while acidic ones dominated in fish fed feed with 2% of urea added.